Hydroclimate of the Indus: Synthesis of the literature relevant to Indus basin hydroclimate processes, trends, seasonal forecasting and climate change

[摘要] The Pakistan water sector faces increased stress given the compounding impacts of a steadily rising population, infrastructural inefficiencies and a changing climate. The Government of Pakistan supports the use of the best available international science to underpin long‐term water sector reforms. This report reviews the literature on Indus basin hydroclimate processes, trends, seasonal forecasting and climate change, focussing on the Upper Indus Basin (UIB). Synthesis of this knowledge informs research that is developing better seasonal forecasting tools to improve river operations, thus helping Pakistan to better manage its water crisis.The majority of Indus water supply is contributed by the glaciated and snow covered sub‐basins of the UIB, within the northern Hindu‐Kush, Karakoram and western Himalayan (HKKH) mountain ranges. The summer monsoon and western disturbances (WDs) are the main climatological drivers of precipitation magnitude and variability in these sub‐basins. The monsoon draws moisture from the Arabian Sea and Bay of Bengal into South Asia, across Pakistan and into the southern UIB during June to September. It is the predominate source of precipitation during this season, coinciding with the period of maximum snow and glacier melt. Hence UIB flow peaks during thisseason. WDs are mid‐latitude low‐pressure systems from the Mediterranean Sea, or even the eastern Atlantic Ocean, together with secondary sources from the Persian Gulf and Arabian Sea.During the October to March period they propagate from west to east across Iran, Iraq, Afghanistan, Pakistan and northern India, interacting with the steep HKKH orography to produce heavy winter snowfalls across the UIB. WDs contribute more to UIB flow than the monsoon. Glacier melt, which is temperature driven, is a significant contributor to UIB flow (~20% of flow).The high altitude regions of the HKKH have limited numbers of stations recording climatological data. Thus data limitations make it difficult to reach firm conclusions regarding hydrological andglaciological response to the climatology of the UIB. It is likely that the precipitation at high altitudes is up to an order of magnitude higher than that recorded in weather stations in lower altitude valley locations. Gridded products are correspondingly impacted by the lack of high altitude station inputs, resulting in reduced confidence in the climatological inputs to hydrological models at high altitudes.Within the limitations of data availability, several climatological and hydrological data studies have presented evidence of trends in climate drivers and hydrological response across the UIB. It isclear that the UIB has warmed over the last century, with increased rates of warming seen in recent decades. Warming trends are greater in winter than summer, with some studies showing summer cooling, and also warming is greater with elevation. Declining snow cover trends have also been linked to warming. Summer cooling may be linked to increased penetration of monsoon precipitation into the UIB.Precipitation trends are less consistent than temperature trends, as various studies have found increasing, decreasing or no trends in different regions of the UIB and for different seasons and time periods. For example, Archer and Fowler (2004) found 1961‐1999 winter precipitation has increased for 17 stations across the UIB; in contrast Bhutiyani et al. (2007) and Bhutiyani et al. (2010) found no trend in winter precipitation with a decreasing trend in monsoon precipitation for the north western Himalayas.Flow trends are a direct response to precipitation and temperature trends, as precipitation determines the amount of accumulated snow cover and temperature controls melt processes (snow and glacier melt). High‐elevation glaciated basin flow correlates with temperature, middle-elevation basin flow correlates with both temperature and precipitation, and lower‐elevation basin flow correlates with seasonal rai...

[发布日期] 2016-02-25 [发布机构] CSIRO

[学科分类] 地球科学(综合)